Figure out what lineup you will be using, and go for treasures that contains those ninjas. Except Naruto and Madara, GNW treasure contains nothing useful for later use, but that's too far to think about it for you, because on the time you will get one of them, you will have 20k pos1 ninja even as f2p. Always good to save 180-220 seals for Roshi, Han, Ay or any other similar ninja, so you have some variation on your lineup. Also from Limited time treasures to get Edo jinchuriki. But as i said, figure your lineup and aim for those ninjas. Don't waste seals without plan.